The present invention relates to both an insulated joint which is formed with a throughhole at its center and which is adapted to be either attached through the wall of a hermetical container of metal, for example, or disposed midway of a metal pipe, and to a method for producing the joint. More particularly, the invention relates to an insulated joint which is suitable for use in a cooling system using a cold liquid such as liquid nitrogen or helium in which a cold liquid passes through the joint with very little heating of the liquid.
Major characteristics required for an insulating joint to be used for the aforementioned purposes are as follows. First, the hermetical sealing characteristics should be quite excellent. The ability to withstand large temperature changes and impact forces should be sufficient that the hermetical sealing characteristics are not adversely affected even by many repetitions of abrupt rises and drops of the temperature. The mechanical impact strength must be sufficient. Moreover, the changes in characteristics with age should be sufficiently little that the reliability of the joint is maintained for a long time. In addition to the aforementioned fundamental requirements, the attachment to the wall of a system and the connection to a metal pipe should be easy. Furthermore, the external size of the joint should be very small for a predetermined flow rate and the price should be low.
Generally, an insulating joint of the aforementioned type utilizes an insulating member sandwiched between two conduits. In such a joint, the most important factor affecting the characteristics enumerated above is this insulating member. The use of an organic material for the insulating member is considered impossible as a practical matter because hermetic sealing characteristics are lowered as the material ages due to repeated temperature changes. In case glass is used for the material, on the other hand, cracking may take place due to abrupt changes in the temperature and the mechanical impact strength of glass is low. If a porcelain material is used and fused by means of metal having a low melting point, the thermal and mechanical impact strengths are low as in the case of glass. Therefore, none of these materials can be used as a practical matter.
Considering the various characteristics thus far described, a most excellent material for the insulating member is a molded glass-mica composition as will be described in detail in the following.
Molded glass-mica as an insulating member can be prepared by heating a mixture of glass powders and mica powders to a temperature sufficiently high to melt the glass so that it will flow under pressure. The melted mixture is pressure molded.
A conventional example of an insulated joint using molded glass-mica as the insulating member will be described with reference to FIG. 1. FIG. 1 is a longitudinal section showing the construction of the joint. In FIG. 1, reference numeral 1 indicates a first tubular member, and reference numeral 2 indicates a second tubular member which is made of a metal such as steel or stainless steel which can withstand a temperature of about 600.degree. C. Reference numerals 1a and 2a indicate joint portions which are to be joined to system walls, conduits or the like by such as by welding or with screws. Reference numeral 3 indicates an insulating member which is made of molded glass-mica and which is disposed to fill a gap 4 thereby to fix the first tubular member 1 and the second tubular member 2 while forming a tight hermetic seal therebetween. The insulating joint thus constructed provides the required characteristics such as the hermetic seal, the ability to withstand temperature changes and mechanical impact forces and long term reliability. However, this joint construction suffers the drawbacks that attachment to a system wall or connection to a metal pipe is quite difficult, that the manufacturing cost thereof is high, and that a high resistance is presented to the passage of a liquid medium through the joint.
In order to further understand the reasons for those defects, a general explanation of the conventional producing method will be given with reference to FIG. 2. FIG. 2 is a longitudinal section showing the molding condition of an insulating joint according to the prior art of which the lefthand half of the figure shows the condition of the joint immediately before a pressure molding process and the righthand half of the figure shows the condition of the joint after the completion of the pressure-molding process. In FIG. 2, reference numerals 1, 2, 3 and 4 indicates the same parts as those of FIG. 1. Reference numeral 5 indicates a splitting wall of two piece construction, for example, reference numeral 6 indicates a mold flask, and reference numeral 7 indicates a supporting member which is composed of a holding portion 7a for holding the second tubular member 2 on the top surface at the center of the holding portion and a cavity 7b in which is later formed an internal insulating portion 3a. Reference numeral 8 indicates an auxiliary member the outer surface of which extends directly from the outer surface of the second tubular member 2 and which is formed with an extending portion 8a for maintaining the two outer surfaces in this relationship. Reference numeral 9 indicates a pressure member which is formed with a throughhole 9a through which the auxiliary member 8 and the second tubular member 2 can pass.
The mold constructed of the aforementioned five parts is used. Reference numeral 10 indicates a preliminary molded member which is prepared by adding water to a mixture of the same glass and mica powders used for the insulating member 3. The wetted mixed powders are molded with a second mold (not shown) into a cylindrical form having a throughhole 10a at its center. The cylindrically shaped powders are next dried.
In the molding process, as shown in the lefthand part of FIG. 2, the split wall 5, the mold flask 6 and the supporting member 7 are assembled. They are then heated to a predetermined temperature together with the auxiliary member 8 and the pressure member 9, neither of which are assembled at this point. Then, the first tubular member 1, the second tubular member 2 and the preliminary molded member 10 are heated to predetermined temperatures. After heating, the first tubular member 1 is first fitted in the gap between the splitting wall 5 and the supporting member 7. Then, the second tubular member 2 is placed on the supporting member 7. The auxiliary member 8 is next placed upon the second tubular member 2. Finally, the preliminary molded member 10 is placed on the first tubular member 1. The pressure member 9 is then placed upon the preliminary molded member 10 and a pressure is applied to the pressure member 9 by a pressure-molding machine. As a result, the material of the preliminary molded member 10 flows to fill up the gap 4 thereby to form the internal insulating portion 3a and an outer insulating portion 3b. The condition at this time is shown in the righthand side of FIG. 2. Due to the flow of the preliminary molded member 10, a lifting pressure is established on the bottom surface of the second tubular member 2 in a region indicated by an arrow 11 which urges the second tubular member 2 upwards. In order to prevent actual movement of the second tubular member 2 of a pressure higher than the lifting pressure should be applied to the auxiliary member 8 thereby to prevent lifting. After the pressure molding has been finished, the mold is cooled to a desired temperature and the mold is disassembled to allow the resulting molding to be removed.
Since the diameter of the center throughhole 2b of the second tubular member is small, the second tubular member is machined to the configuration of the product shown in FIG. 1.
The conventional product thus made by the aforementioned process can sufficiently attain the required characteristics such as the hermetic sealing characteristic and the resistance to temperature change and mechanical impact. However, since the first and second tubular members have different external and internal diameters, attachment of the joint to the system wall, especially if the product is used between metal pipes thereby to provide an insulating function, is quite difficult. On the other hand, even if any device is made such that connection can be made more easily, the resulting difference in the internal diameters necessitated by such a modification leads to an increase in the flow resistance. If this problem is to be avoided, an especially large insulated joint has to be used so that the system is enlarged as a who1e and the price of the product then is excessively high.
Difficulties related to the production of the product will be described. An intense external pressure is applied to the area indicated by the arrow 12 in the righthand portion of FIG. 2 during the pressure molding process. As a result, deformation takes place making the molding process impossible if the thickness of the second tubular member 2 is too small. Therefore, a thick second tubular member 2 has to be used making it necessary that the diameter of the throughhole 2b be enlarged by a machining process after the molding process. As a result, the length of the second tubular member 2 must be restricted.